Jay..I think that the logarithmic feature of PR will require a lot more than text on the site to get to the next level....although it certainly helps in one of the some 100 aspects of the algo, the main path I would be following would be gathering as many quality links from other sites as you can (I think you already know this) as they are what will eventually push you over the top.
Looking at the adult sites that make it to a PR7, which are very few these days as you noticed, either get there through "other methods we wont discuss" or a huge amount of targetted links, which looking at the link sites, would be best in the internal pages level on your site. (just my opinion and I may be wrong but when the internal pages are 2 points lower than the root page, it usually shows the PR of the root page to be at the low end of that PR6)
That said, other than a few small benefits of the PR, I'd be more concerned with adding the text type pages to go for more rankings on keywords to make sales....a lot more important in my book and from personal experience, it doesnt take much PR to get ranked pretty high for some important keywords as long as you have good content
